Chlorides and chloride intrusion have long been known to be detrimental to steel reinforced concrete structures, causing the area around the steel bars to have a reduced pH and the bars to corrode. Corrosion of the bars causes spalling of the concrete leading to failure if costly repairs are not undertaken.
The present invention relates to certain improvements in the electrochemical removal of chlorides from concrete steel reinforced structures. Prior U.S. Pat. No. 4,832,803 discloses a method for removal of such chlorides using an electrode mounted on the structure with a set retarded spray-on material such as retarded gunnite. After the treatment process the gunnite is removed by washing with a stream of water and the electrode is removed. Prior art has also used blown on papier-mache.
The work shown in such prior patent is an attempt to find field utility for chloride removal such as the experiments reported by Slater as mentioned in the text of such U.S. patent and the cited prior art therein. A similar process is shown in prior U.S. Pat. No. 4,865,702 which discloses a variety of electrolytic mediums, including salt solutions. Again however the medium is applied at the beginning of the treatment and removed at the end of the treatment. No effort is made to maintain a saturated pore structure uniformly throughout the treatment process.
Many problems have been encountered in attempting to apply such treatment processes on a full field scale. For example, it has been found that to initiate the treatment, the coating over the electrode has to be hosed down. If it dries out, it has to be hosed down again. Thus, the process may have to be constantly watched or supervised. It has also been found that excessive voltages are required for the treatment to be effective, and that the treatment takes an inordinate amount of time. Moreover, with prior art processes there is no way to add or control chemicals such as cation or anion inhibitors, nor is there any efficient means to calculate the amount of chloride removed. Furthermore, a custom application for each treatment and lack of reusability significantly increases the cost of the treatment.
It has been discovered that such treatments can be cost effective if there is a uniform saturated pore structure between the electrode and steel bar throughout the treatment process, and if the apparatus is prepackaged or partly assembled for easy field assembly and disassembly, and reusable.